Correct installation of reflective-insulation systems can reduce heat loss.

(The following is taken from the Reflective Insulation Manufacturers Association's technical bulletin No. 104, "Reflective Insulations in Duct System Applications.")

Reflective insulation typically performs as a system that incorporates one or more highly reflective (low-emittance) surface(s) adjacent to an enclosed air space.

Reflective insulation is typically installed on the outside of a duct, using spacers to create an enclosed air space between the outer surface of the duct and the low-emittance surface of the reflective insulation. When installed in this manner, reflective insulation can effectively reduce heat loss from ducts and can prevent warm, moist air from being drawn into return ducts and coming into contact with cold duct surfaces.

The key to maintaining a comfortable, energy-efficient living environment in a home or building is to reduce the heat loss in the winter and to minimize cooling loads in the summer. One way to improve the energy efficiency of a home or building is to improve the efficiency of the duct system.

Ducts are usually made from sheet metal or flexible plastic material. A duct system circulates warm and cold air throughout a home or building. Typical duct systems can lose 25 percent to 40 percent of the heating or cooling energy emitted by the central furnace, heat pump or air conditioner. According to the U.S. Environmental Protection Agency, leaking ducts can decrease the overall efficiency of a home's heating and cooling system by as much as 20 percent.

Figure 1. Reflective-insulation system with longitudinal spacers.

Energy losses

Recent research funded by the Department of Energy and the California Institute for Energy Efficiency through the Lawrence Berkeley National Laboratory found that typically, a quarter of the energy (and therefore money) used for heating and cooling is wasted through duct-system energy loss. Sealing ducts can increase the ability of air conditioners, furnaces and heat pumps to evenly heat and cool all of the rooms in a home or building. Using reflective insulation to reduce heat loss during cold seasons and to prevent warm, moist air from being drawn into leaky return ducts during hot, humid seasons can enhance the efficiency of duct systems.

In many places in the country, ducts are located in attics, crawl spaces, garages, basements (unoccupied) and other locations outside the heated or cooled areas of a house. Ducts in these locations not only leak air to and from outside, but also lose heat through the walls of the duct (by heat conduction). Air leaks into and out of ducts at connections within the duct system.

This means that the air that occupants have paid to have heated or cooled escapes from the heating or cooling system and does not heat or cool the home. In addition, air leaks into the heating and cooling system increase the amount of outside air that must be heated or cooled.

Figure 2. Reflective-insulation system with radial spacers.

Installation guidelines

Pre-installation inspection and preparation - In areas where insulation is to be installed, components of the duct system shall be free from defects and leaks. Ex-filtration at joints will cause condensation in the cooling mode and reduced thermal resistance of the insulation system in both modes. If the duct system is found to be faulty, repairs shall be completed prior to the installation of the reflective insulation.

Installation - Reflective-insulation systems designed for use on air-handling systems reduce heat loss or gain to the air in the ducts and prevent condensation due to warm, high-humidity air coming into contact with cold duct surfaces. In order to accomplish these objectives, the manufacturer's installation instructions must be followed. The important factors related to reflective insulation installation are discussed below. A pre-installation inspection is an important first step in the installation process. Ducts with mechanical defects should be repaired before insulation is installed.

Reflective-insulation systems use closed air spaces to provide a major part of the system's resistance to heat flow, or "R-value." Reflective-insulation systems for air-handling systems usually consist of spacer material to provide an enclosed air space between the outside duct surface and the reflective insulation installed around the duct. Various types of spacers are used for this application. The air gap between the duct and the reflective insulation is generally one-half to 1 1/2 inches thick. The spacer design may be either continuous strips or short pieces positioned to ensure the air gap. The specification of the spacer material and method of applying to the duct is an important part of the reflective-insulation system design.

Please refer to the manufacturer's literature for this information. Spacer installation instructions must be followed in order to achieve the labeled system R-value.

The drawings shown in Figure 1 and Figure 2 represent the options for installation of spacer materials.

The following information is intended as a guide only and does not replace the manufacturer's installation instructions.

The reflective insulation shall be handled in accordance with the manufacturer's instructions and should be kept free of extraneous material.

The manufacturer's installation instructions and local building codes should be followed to ensure proper installation. The thermal performance of a reflective-insulation system is based on the maintenance of an enclosed air space between the duct and the adjacent low emittance surface of the reflective insulation.

The thermal performance of a reflective-insulation system depends on adherence to the manufacturer's instructions for spacer positioning, spacer dimensions, spacer material and air-space dimensions.

Consult the manufacturer's installation instructions for the proper method of sealing and fastening seam edges and joints. Use only Underwriters Laboratories' standard No. 181-approved pressure-sensitive tapes and sealants.

The thermal performance of a reflective insulation system will be diminished if there is not a good seal around duct hangers or clamps. Consult the manufacturer's installation instructions for directions on sealing around hangers and clamps.

(For information on "Reflective Insulations in Duct System Applications," contact RIMA at 4519 E. Lone Cactus Drive, Phoenix, AZ 85050; call (800) 279-4123; fax (480) 513-4748; copies are available at on the Internet.)